Oscilloscope Glossary

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2 + 2 channel operation

Two-plus-two channel operation limits the simultaneous display of channels to two of the four channels provided. Channels not displayed can be used to couple a triggering signal to the oscilloscope.  

AC

(Alternating Current) A signal in which the current and voltage vary in a repeating pattern over time.

AC coupling

A type of signal transmission that blocks the DC component of a signal but uses the dynamic (AC) component. Useful for observing an AC signal that is normally normally riding on a DC signal.

Accuracy

The closeness of the indicated value to the true value.

ADC

(Analog-to-Digital Converter) A digital electronic component that converts an electrical signal into discrete binary values.

AMI

A triggering mode where the oscilloscope triggers on "isolated ones" in standard AMI signals (including DS1, DS3, E1, E3, and STS-1).

Acquisition

The process of sampling signals from input channels, digitizing the samples into data points, and assembling the data points into a waveform record. The waveform record is stored in memory. The trigger marks time zero in that process.

Acquisition interval

The time duration of the waveform record divided by the record length. The oscilloscope displays one data point for every acquisition interval.

Aliasing

A false representation of a signal due to insufficient sampling of high frequencies or fast transitions. A condition that occurs when a oscilloscope digitizes at an effective sampling rate that is too slow to reproduce the input signal. The waveform displayed on the oscilloscope may have a lower frequency than the actual input signal.

Alternate Mode

A display mode of operation in which the oscilloscope completes tracing one channel before beginning to trace another channel.

Amplitude

The magnitude of a quantity or strength of a signal. In electronics, amplitude usually refers to either voltage or power.

AND

A logic (Boolean) function in which the output is true when and only when all the inputs are true. On the oscilloscope, that is a trigger logic pattern and state function.

Application Area

• Electronic Design
• Home/Hobbyist
• High Performance
• Manufacturing Test

Area

Measurement of the waveform area taken over the entire waveform or the gated region. Expressed in volt-seconds. Area above ground is positive; area below ground is negative.

Attenuation

The degree the amplitude of a signal is reduced when it passes through an attenuating device such as a probe or attenuator. That is, the ratio of the input measure to the output measure. For example, a 10X probe will attenuate, or reduce, the input voltage of a signal by a factor of 10.

Automatic trigger mode

A trigger mode that causes the oscilloscope to automatically acquire if triggerable events are not detected within a specified time period.

Autoset

A function of the oscilloscope that automatically produces a stable waveform of usable size. Autoset sets up front-panel controls based on the characteristics of the active waveform. A successful autoset will set the volts/div, time/div, and trigger level to produce a coherent and stable waveform display.

Average (acquisition mode)

In this mode, the oscilloscope acquires and displays a waveform that is the averaged result of several acquisitions. Averaging reduces the apparent noise. The oscilloscope acquires data as in the sample mode and then averages it according to a specified number of averages.  

Bandwidth

Bandwidth describes the gain versus frequency limits between an upper and lower frequency. These frequencies are the points where the vertical amplifier voltage gain drops to 70.7% of maximum (3 db down). In modern specifications, bandwidth refers to the highest frequency signal the oscilloscope can acquire with no more than 3 dB (y .707) attenuation of the original (reference) signal. All Tektronix oscilloscopes have a low-frequency response that extends to DC.  

Channel

An input used for signal acquisition. Most Tektronix oscilloscopes have four input channels.

Channel/probe deskew

A relative time delay for each channel. The ability to adjust deskew lets you align signals to compensate for the fact that signals may come in from cables of differing length.

CRT

(Cathode-Ray Tube) An electron-beam tube in which the beam can be focused on a luminescent screen and varied in both position and intensity to produce a visible pattern. The displays on most oscilloscopes use a CRT.

Chop Mode

A display mode of operation in which small parts of each channel are traced so that more than one waveform can appear on the screen simultaneously.

Circuit Loading

The unintentional interaction of the probe and oscilloscope with the circuit being tested, distorting the signal.

CMI

A triggering mode where the oscilloscope triggering isolates positive or negative none pulses and zero pulses in standard CMI signals (including STS-3, STM-1E, DS4, and E4).

Compensation

A probe adjustment for 10X probes that balances the capacitance of the probe with the capacitance of the oscilloscope.

Coupling

The method of connecting two circuits together. Circuits connected with a wire are directly coupled; circuits connected through a capacitor or a transformer are indirectly (or AC) coupled.

Cursors

Paired markers that you can use to make measurements between two waveform locations. The oscilloscope displays the values (expressed in volts or time) of the position of the active cursor and the distance between the two cursors.  

DC (Direct Current)

A signal with a constant voltage and current.

DC coupling

A mode that passes both AC and DC signal components to the circuit. Available for both the trigger system and the vertical system.

Delay by Time

In the Delay by Time triggering mode, the start of signal acquisition is delayed from the main trigger point by a user-definable period of time.

Delay by Events

In the Delay by Events triggering mode, the start of signal acquisition is delayed from the main trigger point by a user-definable number of trigger events.

Delay measurement

A measurement of the time between the middle reference crossings of two different waveforms.

Delay time

The time between the trigger event and the acquisition of data.

Differentiate (Signal Processing)

The capability of an oscilloscope to display a derivative math waveform. The derivative math waveform indicates the instantaneous rate of change of the waveform acquired. One use of derivative waveforms is the measurement of amplifier slew rate.

Digitizing

The process of converting a continuous analog signal such as a waveform to a set of discrete numbers representing the amplitude of the signal at specific points in time. Digitizing is composed of two steps: sampling and quantizing.

Division

Measurement markings on the CRT graticule of the oscilloscope.  

Earth Ground

A conductor that will dissipate large electrical currents into the Earth.

Edge Trigger

Triggering occurs when the oscilloscope detects the source passing through a specified voltage level in a specified direction (the trigger slope).

Envelope

An acquisition mode in which the oscilloscope acquires and displays a waveform that shows the signal's highest and lowest points acquired over many acquisitions.

Equivalent-time Sampling

A sampling mode in which the oscilloscope constructs a picture of a repetitive signal by capturing a little bit of information over many repetitions of the event. For example, Tektronix TDS 500B and 700B models use a type of equivalent-time sampling called random equivalent-time sampling, which uses an internal clock that runs asynchronously with respect to the input signal and the signal trigger. The oscilloscope takes samples continuously, independent of the trigger position, and displays them based on the time difference between the sample and the trigger. Although the samples are taken sequentially in time, they are random with respect to the trigger.  

Fall time

A measurement of the time it takes for the trailing edge of a pulse to fall from a high reference value (typically 90%) to a low reference value (typically 10%) of its amplitude.

FFT (Fast Fourier Transform)

The FFT function enables the oscilloscope to transform a waveform from a display of its amplitude against time to one that plots the amplitudes of the various discrete frequencies the waveform contains. Some uses for FFT capability are measuring harmonic content and distortion in systems, analyzing vibration, testing the impulse response of filters, and identifying noise sources in digital logic circuits.

Focus

The oscilloscope control that adjusts the CRT electron beams to control the sharpness of the display.

Frequency

The number of times a signal repeats in one second, measured in Hertz (cycles per second). The frequency equals 1/period.  

Gated Measurements

A feature that lets you limit automated measurements to a specified portion of the waveform. You define the area of interest using the vertical cursors.

Gigahertz (GHz)

1,000,000,000 Hertz; a unit of frequency.

Glitch

An intermittent error in a circuit.

Glitch positive trigger

Triggering occurs if the oscilloscope detects positive spike widths less than the specified glitch time.

Glitch negative trigger

Triggering occurs if the oscilloscope detects negative spike widths less than the specified glitch time.

Glitch either trigger

Triggering occurs if the oscilloscope detects either positive or negative spike widths less than the specified glitch time.

GPIB (General Purpose Interface Bus)

An interconnection bus and protocol that allows you to connect multiple instruments in a network under the control of a controller. Also known as IEEE 488 bus. It transfers data with eight parallel data lines, five control lines, and three handshake lines.

Graticule

A grid on the display screen that creates the horizontal and vertical axes. You can use it to visually measure waveform parameters.

Ground

1. A conducting connection by which an electric circuit or equipment is connected to the earth to establish and maintain a reference voltage level.
2. The voltage reference point in a circuit.

 

Hardcopy

The ability to save a oscilloscope display in an electronic format useable by a printer or plotter.

Hertz (Hz)

The unit of frequency. One Hertz is equal to one cycle per second.

HF Reject

HF Reject removes the high frequency portion of the triggering signal. Thus, only low frequency components are passed on to the triggering system to start an acquisition. High frequency rejection attenuates signals above 30 kHz.

Hi Res acquisition mode

An acquisition mode in which the oscilloscope averages all samples taken during an acquisition interval to create a record point. That average results in a higher-resolution, lower-bandwidth waveform. That mode only works with real-time, non-interpolated sampling.

Holdoff, trigger

A specified amount of time after a trigger signal that elapses before the trigger circuit will accept another trigger signal. Trigger holdoff helps ensure a stable display.

Horizontal bar cursors

The two horizontal bars that you position to measure the voltage parameters of a waveform. The oscilloscope displays the value of the active (moveable) cursor with respect to ground and the voltage value between the bars.  

InstaVu[TM] acquisition mode

An acquisition mode that increases the waveform capture rate to up to 400,000 waveforms per second. This very fast capture rate greatly increases the probability that runts, glitches, and other short term changes will accumulate in waveform memory. The oscilloscope then displays the waveform at the normal display rate using variable or infinite persistence.

Integrate

The capability of an oscilloscope to display a integral math waveform. The integral math waveform is computed from the acquired waveform. One use of integral waveforms is for measuring power and energy, such as in switching power supplies.

Interleaving

A method by which some oscilloscopes attain higher digitizing speeds. The oscilloscope applies the digitizing resources of unused channels (that is, channels that are turned off) to sample those that are in use (turned on).

Interpolation (Signal Processing)

Generally speaking, a "connect-the-dots" processing technique to estimate what a fast waveform looks like based on only a few sampled points. More specifically, Interpolation refers to the way the oscilloscope calculates values for record points when the oscilloscope cannot acquire all the points for a complete record with a single trigger event. That condition occurs when the oscilloscope is limited to real time sampling and the time base is set to a value that exceeds the effective sample rate of the oscilloscope. The oscilloscope has two interpolation options: linear or sin(x)/x interpolation.

Linear interpolation calculates record points in a straight-line fit between the actual values acquired. Sin(x)/x computes record points in a curve fit between the actual values acquired. It assumes all the interpolated points fall in their appropriate point in time on that curve.  

Kilohertz (kHz)

1000 Hertz; a unit of frequency.  

LF Rejection

LF Rejection removes the low frequency portion of the triggering signal. Thus, only high frequency components are passed on to the triggering system to start an acquisition. Low frequency rejectionn attenuates signals below 80 kHz.

Limit Test

The ability of an oscilloscope to compare an input signal or math waveform to a template waveform. When performing a limit test, the oscilloscope looks for waveforms that fall outside the limits defined by the template waveform. The oscilloscope can be programmed to generate a hardcopy, sound a bell or stop and wait for input from an operator when it finds a waveform that exceeds the template limits.

Logic state trigger

A feature on some oscilloscopes that checks for defined combinatorial logic conditions on channels 1, 2, and 3 on a transition of channel 4 that meets the set slope and threshold conditions. If the conditions of channels 1, 2, and 3 are met then the oscilloscope triggers.

Logic pattern trigger

A feature on some oscilloscopes where the trigger depends on the combinatorial logic condition of channels 1, 2, 3, and 4. Allowable conditions are AND, OR, NAND, and NOR.  

Math

The ability of an oscilloscope to mathmatically manipulate waveforms. The basic functions of waveform math are Add, Subtract, Divide, Multiply, and Invert.

Maximum

Amplitude (voltage) measurement of the maximum amplitude. Typically the most positive peak voltage.

Maximum Input Voltage

The maximum voltage that can be applied to an input channel without damaging the input circuitry.

Mean

Amplitude (voltage) measurement of the arithmetic mean over the entire waveform.

Minimum

Amplitude (voltage) measurement of the minimum amplitude. Typically the most negative peak voltage.

Megahertz (MHz)

1,000,000 Hertz; a unit of frequency.

Megasamples per second (MS/s)

A sample rate unit equal to one million samples per second.

Microsecond

A unit of time equivalent to 0.000001 seconds.

Millisecond (ms)

A unit of time equivalent to 0.001 seconds.  

NAND

A logic (Boolean) function in which the output of the AND function is complemented (true becomes false, and false becomes true). On the oscilloscope, that is a trigger logic pattern and state function.

Negative duty cycle

A timing measurement representing the ratio of the negative pulse width to the signal period, expressed as a percentage.

Negative overshoot measurement

Amplitude (voltage) measurement.

Negative width

A timing measurement of the distance (time) between two amplitude points (the falling-edge middle reference point (default 50%) and the rising-edge middle reference point (default 50%) ) on a negative pulse.

Noise Reject

Noise Rejection reduces the sensitivity of the trigger circuitry. Noise Rejection requires additional signal amplitude for stable triggering, reducing the chance of falsely triggering on noise.

Normal trigger mode

A mode in which the oscilloscope does not acquire a waveform record unless a valid trigger event occurs. It waits for a valid trigger event before acquiring waveform data.

NOR

A logic (Boolean) function in which the output of the OR function is complemented (true becomes false, and false becomes true). On the oscilloscope, that is a trigger logic pattern and state function.

Nanosecond (ns)

A unit of time equivalent to 0.000000001 seconds.

Noise

An unwanted voltage or current in an electrical circuit.

NRZ

A triggering mode where the oscilloscope triggers on rising or falling edges, or any of eight 3-bit serial patterns in NRZ signals (including SONET/SDH, Fibre Channel, FDDI, 143 and 270 Mb/s serial video signals).  

Oscilloscope

An instrument for making a graph of two factors. These are typically voltage versus time. The word oscilloscope comes from "oscillate," since oscilloscopes are often used to measure oscillating voltages.  

Peak - V[p]

The maximum voltage level measured from a zero reference point.

Peak Detect

An acquisition mode in which the oscilloscope saves the minimum and maximum samples over two adjacent acquisition intervals. For many glitch-free signals, that mode is indistinguishable from the sample mode. (Peak detect mode works with real-time, non-interpolation sampling only.)

Peak-to-peak - V[p-p]

The voltage measured from the maximum point of a signal to its minimum point, usually twice the V[p] level.

Peak Detection

An acquisition mode for digital oscilloscopes that lets you see the extremes of a signal.

Peak-to-Peak

Amplitude (voltage) measurement of the absolute difference between the maximum and minimum amplitude.

Period

A timing measurement of the time covered by one complete signal cycle. It is the reciprocal of frequency and is measured in seconds.

Phase

A timing measurement between two waveforms of the amount one leads or lags the other in time. Phase is expressed in degrees, where 360_ comprise one complete cycle of one of the waveforms. Waveforms measured should be of the same frequency or one waveform should be a harmonic of the other.

Pixel

A visible point on the display. The oscilloscope display is 640 pixels wide by 480 pixels high.

Phase

The amount of time that passes from the beginning of a cycle to the beginning of the next cycle, measured in degrees.

Positive duty cycle

A timing measurement of the ratio of the positive pulse width to the signal period, expressed as a percentage.

Positive overshoot

Amplitude (voltage) measurement.

Positive width

A timing measurement of the distance (time) between two amplitude points (the rising-edge middle reference point (default 50%) and the falling-edge middle reference point (default 50%)) on a positive pulse.

Posttrigger

The specified portion of the waveform record that contains data acquired after the trigger event.

Pretrigger

The specified portion of the waveform record that contains data acquired before the trigger event.

Probe

An oscilloscope input device, usually having a pointed metal tip for making electrical contact with a circuit element and a flexible cable for transmitting the signal to the oscilloscope.

Pulse

A common waveform shape that has a fast rising edge, a width, and a fast falling edge.

Probe compensation

Adjustment that improves low-frequency response of a probe.

Pulse trigger

A trigger mode in which triggering occurs if the oscilloscope finds a pulse, of the specified polarity, with a width between, or optionally outside, the user-specified lower and upper time limits.  

Quantizing

The process of converting an analog input that has been sampled, such as a voltage, to a digital value.  

Real-time Sampling

A sampling mode where the oscilloscope samples fast enough to completely fill a waveform record from a single trigger event. Use real-time sampling to capture single-shot or transient events.

Record Length

The number of waveform points used to create a record of a signal.

Reference memory

Memory in a oscilloscope used to store waveforms or settings. You can use that waveform data later for processing. The oscilloscope saves the data even when the oscilloscope is turned off or unplugged.

Rise Time

The time taken for the leading edge of a pulse to rise from its minimum to its maximum values (typically measured from 10% to 90% of these values).

RMS

Amplitude (voltage) measurement of the true Root Mean Square voltage.

Roll Mode

A signal acquisition mode which displays acquired waveform data without waiting for the acquisition of a complete waveform record. For example, when a sweep is 10 divisions long and the sweep rate is 1 second per division, 10 seconds are required to fill the waveform record. Without roll mode you must wait 10 seconds to see that the position control is set wrong. With roll mode, you can start seeing results almost immediately.

Runt trigger

A triggering mode in which the oscilloscope triggers on a runt. A runt is a pulse that crosses one threshold but fails to cross a second threshold before recrossing the first. The crossings detected can be positive, negative, or either.  

Sample

The oscilloscope creates a record point by saving the first sample during each acquisition interval. Sample mode is the default acquisition mode.

Sample interval

The time interval between successive samples in a time base. For real-time digitizers, the sample interval is the reciprocal of the sample rate. For equivalent-time digitizers, the time interval between successive samples represents equivalent time, not real time.

Sampling

The process of capturing an analog input, such as a voltage, at a discrete point in time and holding it constant so that it can be quantized. Two general methods of sampling are: real-time sampling and equivalent-time sampling.

Screen

The surface of the CRT upon which the visible pattern is produced - the display area.

Setup/Hold

A triggering mode in which the oscilloscope triggers when a data source changes state within the setup or hold time relative to a clock source. Positive setup times precede the clock edge; positive hold times follow the clock edge. The clock edge may be the rising or falling edge.

Signal Generator

A test device for injecting a signal into a circuit input; the circuit's output is then read by an oscilloscope.

Signal Processing

With respect to oscilloscopes, this refers to functions which are performed by signal processing hardware/software. For example, signal measurements (rise time, overshoot, period, etc), FFTs, Integration and Differentiation functions are signal processing functions.

Sine Wave

A common curved wave shape that is mathematically defined (by the value of the sine function).

Single Shot

A signal measured by an oscilloscope that only occurs once (also called a transient event).

Single Sweep

A trigger mode for displaying one screenful of a signal and then stopping.

Slew Rate

A triggering mode in which the oscilloscope triggers based on how fast a pulse edge traverses (slews) between an upper and lower threshold. The edge of the pulse may be positive, negative, or either. The oscilloscope can trigger on slew rates faster or slower than a user-specified rate.

Slope

The direction at a point on a waveform. You can calculate the direction by computing the sign of the ratio of change in the vertical quantity (Y) to the change in the horizontal quantity. The two values are rising and falling.

Sweep

One horizontal pass of an oscilloscope's electron beam from left to right across the CRT display.

Sweep Speed

The rate at which the sweep moves across the display. The sweep speed is expressed in units of time per division, for example, 5 ms/div.  

Time Base

Oscilloscope circuitry that controls the timing of the sweep. The time base is set by the Horizontal control.

Time Base Accuracy

The closeness of the indicated time value to the true value.

Time Base Range

The range of values to which the horizontal deflection factor can be set.

Timeout trigger

A trigger mode in which triggering occurs if the oscilloscope does NOT find a pulse, of the specified polarity and level, within the specified time period.

Trace

The visible shapes drawn on a CRT by the movement of the electron beam.

Transducer

A device that converts a specific physical quantity such as sound, pressure, strain, or light intensity into an electrical signal.

Transient

A signal measured by an oscilloscope that only occurs once (also called a single-shot event).

Trigger

The circuit that initiates a horizontal sweep on an oscilloscope and determines the beginning point of the waveform. The trigger point is an event that marks time zero in the waveform record.

Triggering

Triggering Coupling

Describes the circuitry used to connect the trigger source to the trigger circuit. Several types of coupling are available: HF Reject, LF Reject, Noise Reject, AC, and DC. The different types of coupling provide improved triggering performance depending on the characteristics of the trigger source.

Trigger Holdoff

A control that inhibits the trigger circuit from looking for a trigger level for some specified time after the end of the waveform.

Trigger Level

The voltage level that a trigger source signal must reach before the trigger circuit initiates a sweep.  

Vertical bar cursors

The two vertical bars you position to measure the time parameter of a waveform record. The oscilloscope displays the value of the active (moveable) cursor with respect to the trigger and the time value between the bars.

Vertical Accuracy

The closeness of the indicated signal voltage to the true value.

Vertical Resolution

The number bits of bits used to digitize the input signal. An 8-bit digitizer can resolve a signal into 255 levels.

Vertical Sensitivity

The range of values to which the vertical deflection factor can be set.

Volt

The unit of electric potential difference.

Voltage

The difference in electric potential, expressed in volts, between two points.  

Waveform

A graphic representation of a voltage (which can represent other quantities such as temperature) varying over time.

Waveform Point

A digital value that represents the voltage of a signal at a specific point in time. Waveform points are calculated from sample points and stored in memory.

Waveform interval

The time interval between record points as displayed.  

XY format

A display format that compares the voltage level of two waveform records point by point. It is useful for studying phase relationships between two waveforms.  

YT format

The conventional oscilloscope display format. It shows the voltage of a waveform record (on the vertical axis) as it varies over time (on the horizontal axis).  

Z-axis

The signal in an oscilloscope that controls electron-beam brightness as the trace is formed.